The present invention relates to a method of fixing an optical element wherein the optical element is bonded and fixed on a fixing member by optical-curing adhesive, and to a method to manufacture an optical module.
In the past, to bond and fix an optical element such as a pick up lens and a micro lens used for an optical communication module on a fixing member such as a lens barrel, after applying UV curing adhesive, UV was radiated from a light source to the UV curing adhesive (hereinafter called UVA) so as to fix the optical element on the fixing member. For example, as shown in FIG. 14, to fix lens 100 on lens barrel 200, UVA was applied on collar-shaped retaining surface 220 in metal lens barrel 200 and adhesive layer 290 is formed by radiating UV from nozzle 30a of UV light source 30 to lens 100 in the status wherein lens 100 is positioned so that its surface 150 faces retaining surface 220. Meanwhile, it is a merit in terms of cost and lightweight that the optical element such as lens 100 is made of resin material.
Also, the Patent Document 1 below discloses an optical disc member adhering method in which UV is radiated through a filter that intercepts UV having a wavelength of not more than 290 nm so that the durability of adhering force is improved without deteriorating each member of the optical disk by UV when bonding the optical dick members by using UVA.
In the Patent Document 1, as shown in FIG. 4 and FIG. 7 of the document, a glass plate to intercept the light having wavelength of not more than 290 nm is placed on a disk substrate where adhesive is applied in between, and in a status wherein a hollow cylindrical weight made of stainless steel is placed on the glass plate, a plurality of optical fibers are arranged on the outer circumference of the stuck and at the center hole so as to radiate UV from an UV radiation device to the glass plate through each optical fiber.
(Patent Document 1) Unexamined Japanese Patent Application Publication No. Tokkaihei 03-198235
An experimental test performed by inventors of the present invention clarified that it is necessary to radiate UV for a certain period of time to harden UVA, however on the other hand, if UV light is irradiated to the optical element for more than 10 sec, a temperature of the optical element will increase considerably and there is caused a bad effect such as deformation of the lens surface of the optical element, in case an optical element such as a lens is made of resin material. Also it was found that a thickness of adhesive layer will be even, by applying pressure to an adhesion surface where the UVA is applied while the adhesive is hardened by radiating UV.
However, in case, a micro lens having an outer diameter of 4 to 5 mm is fixed by an adhesive on such a lens barrel as shown in FIG. 14, the only way of radiate UV on the adhesive is to radiate UV through the lens because the metal lens barrel is not light-transmissive. It is considerably difficult to arrange a weight in the lens barrel and to radiate UV through the optical fibers arranged in the center hole and on the circumference of the weight as shown in FIG. 4 and FIG. 7 in the Patent Document 1. Also the structure to arrange the weight and the optical fibers is complicated, thus, the process of hardening adhesive is time-consuming, which lowers productivity.